Gold alloy plating process and solution

ABSTRACT

A GOLD ALLOY ELECTROPLATING PROCESS AND SOLUTION IS DISCLOSED WHEREIN THE SOLUTION CNSISTS ESSENTIALLY OF FROM ABOUT 12 TO ABOUT 38 GRAMS OF GOLD AS POTASSIUM AUROCYANIDE, FROM ABOUT 10 TO ABOUT 150 GRAMS OF MAGNESIUM ACETATE. FROM ABOUT 0 TO ABOUT 100 GRAMS OF A SALT OF AN ORGANIC ACID HAVING A CATION SELECTED FROM THE GROUP CONSISTING OF ALKALI METHAL AND AMMONIUM IONS, SAID ACID BEING SELECTED FROM THE GROUP CONSISTING OF ACETIC AND CITRIC, AND FROM ABOUT .005 TO ABOUT .400 GRAM OF A SOLUBLE METAL SOURCE SELECTED FROM THE GROUP CONSISTING OF THE SOURCES OF COBALT AND NICKEL OR MIXTURES THEREOF, RESPECTIVELY, PER LITER OF SOLUTION. THE SOLUTION HAS A PH OF FROM ABOUT 3.6 TO ABOUT 4.2 AND CN BE SATISFACTORILY EMPOLYED AT TEMPERTURES WITHIN AND RANGE OF FROM ABOUT 70* TO ABOUT 120*F.

May 7, 1974 I. EDSON E AL V GOLD ALLOY PLATING PROCESS AND SOLUTION Filed Jan. 29, 1973 F O 9/ l i w 2 I H W p SM D5 mp M5 R w L x. O O. O O mOU &

United States Patent Ofiice Patented May 7,, 1974 3,809,628 GOLD ALLOY PLA'I'ING PROCESS AND SOLUTION Gwynne I. Edson, Russell, and Keith R. Reynolds, Warren, Pa., assignors to GTE Sylvania Incorporated, Seneca Falls, N.Y.

Filed Jan. 29, 1973, Ser. No. 327,397 Int. Cl. C23b 5/42 US. Cl. 204-43 G 7 Claims ABSTRACT OF THE DISCLOSURE A gold alloy electroplating process and solution is disclosed wherein the solution consists essentially of from about 12 to about 38 grams of gold as potassium aurocyanide, from about to about 150 grams of magnesium acetate, from about 0 to about 100 grams of a salt of an organic acid having a cation selected from the group consisting of alkali metal and ammonium ions, said acid being selected from the group consisting of acetic and citric, and from about .005 to about .400 gram of a soluble metal source selected from the group consisting of the sources of cobalt and nickel or mixtures thereof, respectively, per liter of solution.

The solution has a pH of from about 3.6 to about 4.2 and can be satisfactorily employed at temperatures within the range of from about 70 to about 120 F.

BACKGROUND OF THE INVENTION This invention relates to gold alloy electroplating solutions and to processes incorporating such solutions. More specifically, the invention relates to solutions which may be operated at room temperature.

Many of todays gold alloy plating baths are comprised of aqueous solutions containing potassium aurocyanide, KAu(Cn) as the source of gold. This particular complex salt of gold is preferred due to its greater solubility in water. Baths of this type most usually operate with a cathode current density ranging from about 3 to 10 amperes per square foot and at a temperature range of approximately 100 to 120 F. Accordingly, the control of temperature is vital to the electroplating process because of its eliects on variables of the solution such as conductivity, current efficiencies, nature of the deposit, and stability. Previous methods for heating the solution include heating coils in the tank itself, circulating the. solution through various heat exchangers, utilization of electric immersion heaters, and even heating the plating tanks by open gas flames positioned beneath the tank. As can be appreciated, a distinct advantage to the above process would be the operation of the bath at normal room temperature (70 F.) thereby necessitating a minimum of thermostatic or similar regulation of the previously described heating apparatus.

Additionally, a much desired result in the operation of gold alloy plating baths has been the maintenance of relatively constant deposit hardness values. In many previous processes, stable hardness readings varied most readily with only minor alterations in current density, pH, and temperature, as well as the content of the alloying element in the deposit.

It is believed, therefore, that a gold alloy plating solution which could be operated at normal room temperature and could maintain relatively constant deposit hardness values during minor alterations to the solution such as current density, pH, temperature, and deposit alloy element content, would be an advancement in the art.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore a primary object of this invention to provide an improved gold alloy electroplating process and solution therefore.

It is another object of this invention to provide an improved gold alloy electroplating process and solution that are simple and reliable in operation and relatively inexpensive to utilize.

Still another object of this invention is to provide a process and solution as described above which can be readily operated at room temperature.

An even further object of this invention is to provide the above described process and solution which maintains a relatively stable deposit hardness during minor alterations to such variables as current density, temperature, pH, and content of the alloying element in the deposit.

In accordance with one aspect of the invention, there is provided a gold alloy electroplating solution consisting essentially of from 12 to about 38 grams of gold as potassium aurocyanide, from about 10 to about 150 grams of magnesium acetate, from about 0 to about 100 grams of a salt of an organic acid having a cation selected from the group consisting of alkali metal and ammonium ions, said acid being selected from the group consisting of acetic and citric and from about .005 gram to about .400 gram of a soluble metal source selected from the group consisting of the sources of cobalt and nickel or mixtures thereof, respectively, per liter of aqueous solution to provide a pH of from about 3.6 to about 4.2.

In accordance with another aspect of this invention, there is provided a gold alloy electroplating process comprising immersing the surface of a substrate to be plated in an aqueous solution having a concentration of gold as potassium aurocyanide of from about 12 to about 38 grams per liter of solution, from about 10 to about 150 grams per liter of magnesium acetate, from about 0 to about 100 grams per liter of a salt of an organic acid having a cation selected from the group consisting of alkali metal and ammonium ions, said acid being selected from the group consisting of acetic and citric, and from about .005 gram to about .400 gram per liter of a soluble metal source selected from the group consisting of the sources of cobalt and nickel or mixtures thereof wherein the pH of the solution is maintained from about 3.6 to about 4.2 and the temperature is maintained from about 70 F. to about 120 F. The process is achieved by passing an electrical current through the solution in which the substrate serves as the cathode. A non-consumable anode is utilized.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention,

. together with other and further objects, advantages and 3 r capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings.

By the present invention, gold alloy electrolplating baths are disclosed which provide for deposition of bright gold alloy having a composition of from 99 to 99.95% gold with the balance cobalt or nickel. Magnesium has been detected in minute quantities in the deposits but it has not been determined whether or not it is alloyed. By providing predetermined amounts of magnesium acetate in the bath solutions, the baths possess the desired feature of being readily operable at normal room temperature (70 F.). Additionally, the use of magnesium in the electrolyte allows for relatively stable deposit hardness readings despite minor alterations to variables of the solutions such as temperature, pH, current density, and alloy element content.

The gold concentration is from about 12 to about 38 grams per liter with potassium aurocyanide, KAu(Cn) as the source of gold used. Magnesium acetate is combined in the solution from about 10 to about 150 grams per liter, from about to about 100 grams per liter are added of a salt of an organic acid having a cation selected from the group consisting of alkali metal and ammonium ions, said acid being selected from the group consisting of alkali metal and ammonium ions, said acid being selected from the group consisting of acetic and citric, and from about .005 to about .400 gram per liter of a soluble metal source selected from the group consisting of the sources of cobalt and nickel or mixtures thereof is added.

By soluble is meant a metal source which is soluble to the extent of at least 1 gram per liter of solution at a pH of approximately 4.0 when the solution is maintained at 70 F. Typical examples of such sources include cobalt sulfate and nickel sulfate or salts of inorganic acids such as nitric or hydrochloric. Additionally, salts of organic acids such as acetic or citric are suitable.

Suitable examples of salts of the organic acid described above include potassium acetate, sodium acetate, and ammonium acetate. It is to be understood, however, that several others are acceptable and that the invention is not limited to these listed.

The process involves immersing the substrate in the previously described electroplating solution, maintaining the temperature from about 70 F. to about 120 F. and passing an electric current from a non-consumable anode through the solution to provide a current density of from about 1 to about 24 amperes per square foot at the substrate to be plated. As described, gold alloy deposits are attained having a purity in excess of 99% such as 99.95% gold with the balance cobalt or nickel. Magnesium has been detected in minute quantities in the deposit but it has not been determined whether or not it is alloyed. Cathode efiiciencies of from about 20 to 25% are attained.

EXAMPLE I An aqueous solution having the following concentrations of ingredients is prepared:

G./l. Potassium gold cyanide 12.5 Magnesium acetate 100 Cobalt .030 pH: 3.8.

EXAMPLE II A preferred aqueous solution of the present invention consists essentially of the following concentration of ingredients:

G./l. Potassium gold cyanide 25 Magnesium acetate 50 Potassium acetate Cobalt 0.01

The solution is preferably operated at a temperature of about 100 F. with a cathode density of between about 5 and 12.5 amperes per square foot. Full bright deposits have been obtained however at current densities approaching 20 amperes per square foot. At the above prescribed values, the plating rate of gold is approximately .4 mil per hour, the cathode efiiciency is approximately 25%, and the Baum density value is about 12.5, measured at 70 F. As can readily be seen, the solution of Example H differs from that of Example I due to the addition of the alkali metal acetate. As stated, this solution is preferred because of the improved current carrying capacity as a result of the alkali metal acetate addition. Additionally, potassium acetate is preferred as this component be.- cause it is compatable with potassium gold cyanide.

With particular reference to the drawings, in FIG. 1 there is shown the overall effect on some of the variables of the solutions of Example II. ,More specifically, there is illustrated the changes occurring between the pH values and cobalt in solution percentages as the current densities and solution temperatures are varied. As shown, these alterations result in the amount of cobalt being altered only slightly. This has the additional desired feature, as shown in FIG. 2, of assuring only minor corresponding changes in the deposit hardness values. As seen, the percent cobalt in deposit (resulting from that in solution) produces only a minor change in the knoop hardness readings for the deposits thereby resulting in relatively stable values for these readings.

- Thus, there has been shown and described a gold alloy plating solution and process for incorporating same which is readily operable at normal room temperature. The solution additionally provides relatively stable deposit hardness readings despite minor alternations to some of the variables of the solution.

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims;

What is claimed is:

1. An aqueous gold alloy electroplating solution consisting essentially-of from about 12 to about 38 grams of gold as potassium aurocyanide, from about 10 to about grams of magnesium acetate, from about 0 to about 100 grams of a salt of an organic acid having a cation selected from the group consisting of alkali metal and ammonium ions, said acid being selected from the group consisting of acetic and citric, and from about .005 to about .400 gram of a soluble metal source selected from the group consisting of the sources of cobalt and nickel or mixtures thereof, respectively, per liter of solution to provide a pH of said solution of from about 3.6 to about 4.2-.

2. The solution according to claim 1 wherein said salt is potassium acetate.

3. The solution according to claim 1 wherein said salt is sodium acetate.

4. The solution according to claim 1 wherein said salt is ammonium acetate.

5. The solution according to claim 1 wherein said soluble metal source is cobalt.

6. The solution according to claim 1 wherein said solu ble metal source is nickel.

6 7. A process for gold alloy electroplating a substrate passing an electric current through said solution using comprising: a non-consumable anode and said substrate as a immersing a substrate in an aqueous gold alloy electrocathode and to provide a current density up to about plating solution consisting essentially of from about 20 amperes per square f 12 to about 38 grams per liter of solution of gold as 5 potassium aurocyanide, from about to about 150 References Cited grams per liter of magnesium acetate, from about 0 UNITED STATES PATENTS to about 100 grams per liter of a salt of an organic acid having a cation selected from the group consist- 25,883 10/1965 et a1 20443 G ing of alkali metal and ammonium ions, said acid be- 10 3,716,463 2/1973 Blck et a1 204 43 G ing selected from group consisting of acetic and OTHER REFERENCES citric, and from about .005 to about .400 gram per liter of a soluble metal source selected from the group consisting of the sources of cobalt and nickel or mixtures thereof, to provide a pH of from about 3.6 to GERALD L KAPLAN Primary Examiner about 4.2;

maintaining the temperature of said solution from about F. to about F.; and

Abner Brenner, Electro Deposition of Alloys, vol. II, pp. 186-187 (1963), T8693 B7 02.

3 UNITED STATES PATENT OFFICE I CERTIFICATE OF CORRECTION Patent No. 3 9, Dated May 7, 1974 hvenmfls) Gwynne I. Edson and Keith R. Reynolds It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, Line 48: Y 124 amperes" should read 20 amperes Column 3,' Line 72: "plate rate" should read plating I rate Q l Column ,4, Line 44: "alternations" should read i i alterations Claim 7, Line lli "from group" should read from the group Signed and sealed this 1st day of October 1974.

(SEAL) Attest:

C. MARSHALL DANN Commissioner of Patents MCCOY M. GIBSON 'JR. Attesting Officer 

